High-Speed Photography of Rapid Air Currents and Shock Waves by Means of High-Frequency High-Voltage Sparks

The Bömelburg, Weske and Herzog method has been perfected for practical application in wind-tunnel work with 0.8-to 20-in. sparks. A pulse transformer of novel design permits powers up to 40 megawatts peak during each flash at up to 50,000 controlled discharges/sec. Higher rates are possible under free-running conditions. The discharge duration is 0.3 to 1 μsec. — Strobokin-controlled ultra-rapid spark discharges at 2000 to 300,000/sec are fed into the primary of a special pulse transformer whose essential component is a laminated sheet-metal core of hypersile sheets with Hostaphan insulation. A voltage of approximately 5 ko per turn on the primary winding gives a steep voltage step-up at the secondary, which with 75 turns, for example, produces a no-load voltage of 300 kv. — Owing to the short spark-discharge time, no picture blue results even at air speeds of several thousand fast per second. Although the luminance of the sparks is sufficient for high-speed photography, practical experience shows that their low energy does not cause thermodynamic disturbance of the airflow under observation. The lowest possible spark rate where no deionization occurs is 2000/sec. At 1-mm spark spacing, this corresponds to an air velocity of 2 m/sec, whereas the maximum spark rate of 300,000/sec at 20 mm from spark to spark corresponds to an air velocity of 6 km/sec, i.e. approximately Mach 18. Also, patterns of explosion and detonation shock waves and their subsequent eddy current: can be traced by the spark method outlined above.

Print ISSN

0361-4573

Published

1962-03

Content type

Original Research

DOI

10.5594/J16889